As is well known, an increasingly accepted trend of late for electric and electronic gadgets is a requirement for a more accurate load current control in controlling operations thereof. In order to discriminate whether a load current is accurately outputted in relation to a target value, it is necessary to be equipped with a current detecting circuit where the load current is fed back for detection by way of a closed loop method.
As illustrated in FIG. 1, a current detecting circuit according to the prior art includes a current transformer (CT) for receiving a load current to transform same to a small current of easy measurement, a resistor (R1) disposed for establishing an output voltage level of the secondary winding side of the current transformer (CT) as a designed value, a diode (D1) and a capacitor (C1) for half-wave rectifying and smoothening the alternating current output of the secondary winding side of the current transformer (CT) to thereby detect a peak value of a measured current, and an operational amplifier (OA) for buffering the output in relation to the peak value of the measured current detected by the diode (D1) and the capacitor (C1).
Current detection circuits adopted in cookers such as induction heating cookers and the like for heating food contained in cooking containers by flowing current on coils for generation of heat are easily exposed to high heat, whereby the entire temperature of the circuits is increased. An element most sensitive to temperature in the current detection circuits is a diode, and it is a well-known fact that a backward leakage current is increased in the diode as the temperature therein rises.
An ideal forward current (A) flowing in a diode can be explained by FIG. 2(a). However, when the temperature is raised due to the influence of the surrounding temperature, a leakage current (ΔA) flowing backward in the diode is increased to thereby decrease the forward current (A′) flowing in the diode (A′=A−ΔA).
In other words, there is a drawback in that an error can occur in the peak value of the load current detected by the diode and the capacitor due to changes of the forward current (A′) flowing in the diode.